1. Field of the Invention
This invention relates to improvements in the encasing of pipes or electrical cables and, more particularly, to a method and apparatus for allowing pipes and cables to be floated into and out of a casing for installation and replacement purposes once the casing has been emplaced.
2. Description of the Prior Art
In a laying of pipelines or the placement of electrical cables in a casing, gut lines have been used in the past to pull pipes and cables through casings only when the casings have been empty. As a result, friction forces limit the length of the lines that can be pulled through such a "dry" casing.
Other attempts have been made to pull lines, such as a pipe or electrical cable through a casing. For instance, U.S. Pat. No. 4,232,981 describes a technique in which beads are mixed with a liquid, such as water, in a casing to reduce dry friction when a pipe or electrical cable is to be pulled over a limited distance through the casing itself. A technique of pulling and sealing a polyethylene liner in a steel pipe is described in an article entitled "New Way To Protect High Pressure Lines" published in Pipeline Industry, March 1981. This publication indicates that friction limits the length of pull to about 2500 feet.
Because of the drawbacks of the techniques mentioned above, a need has existed for an improved casing method and apparatus which allows one or more pipes or cables to be placed in a relatively long casing in a minimum of time to minimize construction costs yet the pipe or cable, once encased, can be readily removed for repair or replacement.